OpenCV/opencv/modules/gapi/samples/api_example.cpp

#include <opencv2/videoio.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/gapi.hpp>
#include <opencv2/gapi/core.hpp>
#include <opencv2/gapi/imgproc.hpp>

int main(int argc, char *argv[])
{
    cv::VideoCapture cap;
    if (argc > 1) cap.open(argv[1]);
    else cap.open(0);
    CV_Assert(cap.isOpened());

    cv::GMat in;
    cv::GMat vga      = cv::gapi::resize(in, cv::Size(), 0.5, 0.5);
    cv::GMat gray     = cv::gapi::BGR2Gray(vga);
    cv::GMat blurred  = cv::gapi::blur(gray, cv::Size(5,5));
    cv::GMat edges    = cv::gapi::Canny(blurred, 32, 128, 3);
    cv::GMat b,g,r;
    std::tie(b,g,r)   = cv::gapi::split3(vga);
    cv::GMat out      = cv::gapi::merge3(b, g | edges, r);
    cv::GComputation ac(in, out);

    cv::Mat input_frame;
    cv::Mat output_frame;
    CV_Assert(cap.read(input_frame));
    do
    {
        ac.apply(input_frame, output_frame);
        cv::imshow("output", output_frame);
    } while (cap.read(input_frame) && cv::waitKey(30) < 0);

    return 0;
}